1. Field of the Invention
The present invention relates generally to a photosensitive drum earthing mechanism, and more particularly, to a photosensitive drum earthing mechanism which is most suitable for a photosensitive drum of such a type that power is transmitted through an engaging clutch to an image carrier formed of a cylindrical conductive member having an insulating layer on its whole surface.
2. Description of the Related Art
In general, the photosensitive drum of this type is widely used for an image forming section in an image forming apparatus for developing an electrostatic latent image into a toner image. In recent years, in order to unitize the image forming section, the image forming section is at least provided with a unit on which the photosensitive drum is detachably mounted. Such a photosensitive drum on the unit is engaged with a main body through clutch members so disposed respectively on the photosensitive drum and the main body as to connect or disconnect both elements. The torque is transmitted from the main body of the image forming apparatus to the photosensitive drum at the connected state.
The photosensitive drum comprises a cylindrical image carrier made of a conductive material, a bearing portion fixed on both ends of the image carrier, and a supporting pin made of a conductive material which is connected to the bearing portion to carry the image carrier. Since the image carrier and the bearing portion are electrically insulated from each other, an earthing structure for electrically earthing the image carrier is required.
Employed conventionally is an earth plate which comprises a connecting claw electrically connected to the image carrier by contacting with a conductive material portion of the cylindrical image carrier from the inner peripheral wall of the image carrier and a bearing supporting portion receiving a tip end of a supporting pin for carrying a drum in a state where it is brought into sliding contact with the supporting pin. Earth plate is fixed to the image carrier to electrically connect the image carrier and the supporting pin to each other (Japanese Examined Patent Publication No. 4-45828).
In the photosensitive drum earthing mechanism of the foregoing construction, a member on the drum side and a member on the image forming apparatus side are electrically connected to each other by only a contact portion between the bearing supporting portion of the earth plate and the tip end of the supporting pin which are in sliding contact with each other. Therefore, it becomes difficult to obtain a sufficient contact area, resulting in an unstable connected state.
Accordingly, what is really needed is a photosensitive drum earthing mechanism capable of electrically connecting the members on the drum side and the image forming apparatus side to each other reliably.